The objectives of this work are: to delineate antigens of possible significance to the pathogenesis of rheumatoid arthritis (RA) on RA-derived synovial fibroblasts or in RA sera and synovial fluids; and to isolate, characterize and attempt to determine specificities of antibody produced in inflammed rheumatoid synovial tissue. The distribution of antigens of RA synovial fibroblasts grown in vitro is determined by the indirect immunofluorescence test using antisera of known specificities and rabbit anti-synovial fibroblast sera, both unabsorbed and at different stages of absorption. Preparations of antibody from RA synovial tissues have been isolated and their activities against several known antigens and against RA-derived antigens are being determined.